The partial discharge and breakdown characteristics of insulating tapes immersed in liquid nitrogen

Electrical power apparatus operating at cryogenic temperatures offers advantages over conventional equipment and research is continuing to produce superconducting generators and cables in addition to cryoresistive cables. Although there have been a limited number of studies of the behaviour of electrical insulation for such equipment,
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the operating stresses have not been evaluated and little is known of the ageing mechanisms. This paper describes the initial results of a project to determine suitable operating stresses and to study the deterioration of polymeric tapes immersed in a cryogenic fluid while subjected to high electric stresses. Partial discharge and breakdown characteristics of fibrous insulating sheets with and without artificial cavities are reported.